Method for mass producing partial width linear tape recording head

ABSTRACT

A dimple magnetic recording head in a transducer assembly for linear tape drives haviang a flat transducing surface extending laterally a partial width of the magnetic recording tape is mass produced by lapping a row of transducers on a substrate to form a flat transducing surface. The row of substrate elements is then diced into separate substrate elements. Two parallel, spaced apart tape support surfaces are provided extending laterally the full width of the tape, and one of the diced substrate elements is mounted intermediate the tape support surfaces with the flat transducing surface exposed for forming a tape facing surface.

This is a Divisional application of Ser. No. 08/896,356, filed Jul. 18,1997 now U.S. Pat. No. 5,883,770, issued Mar. 16, 1999.

FIELD OF THE INVENTION

This invention relates to magnetic tape recording heads, and, moreparticularly, to tape heads that span only a portion of the width of thetape.

BACKGROUND OF THE INVENTION

Conventional recording heads for linear tape drives have smalltransducers incorporated into a large head assembly to span the fullwidth of the tape. For recording heads fabricated using thin film wafertechnology, this requires that the head either be fabricatedindividually on a wafer which is at least as wide as the recording tapeand lapped individually to the proper shape, or be fabricated as a smallpart and assembled with larger pieces and the full assembly lappedindividually to the proper shape.

The conventional shape of a tape head comprises a cylindrical or complexcontour which is critical in maintaining the moving tape at the desiredhead to transducer spacing (called “contact” or “near contact”recording). The contact, or near contact, spacing is maintained bycontrolling the contour shape to “bleed”, “skive” or “scrape” theboundary layer of air carried by the tape away before encountering thetransducer to prevent the tape from “flying”, or losing contact with thetransducer.

The spacing between the magnetic head and the magnetic tape is crucialso that the recording gap of the transducer, which is the source of themagnetic recording flux, is in intimate or near contact with the tape toeffect efficient signal transfer for recording. The spacing is alsocrucial so that the playback element is in intimate or near contact withthe tape to provide effective coupling of the magnetic field from thetape to the playback element.

The full width of the tape in the prior art is contacted by the headassembly to prevent steering the moving tape as the head assembly ismoved to access different data tracks. In addition, when a short spanhead is near an edge of the tape, the tape, without support, tends tolift from the head as the result of upward flex curvature as it travelsover the protruding head. Thus, a wide head is used to provide supportfor the tape when the recording element is positioned near an edge ofthe tape. Even with full width support, there is an antielastic bendingeffect that tends to lift the tape off the head near the edge of thetape.

FIG. 1 illustrates a conventional linear tape drive recording head 10. Asmall transducer 11 is incorporated into a large unit 12 to span thefull width of the tape 13. FIG. 2 illustrates an example of one methodof fabricating a conventional linear tape drive recording head of FIG. 1using thin film wafer technology. In FIG. 2a, an individual chip 14 isassembled with wings 15 and 16 and closure 17 and glued together to forma full assembly which is shown in an end view in FIG. 2b. A portion ofthe top surface of the full assembly is then ground away to form theassembly shown in FIG. 2c, leaving a rooftop 18. The entire assembly isthen individually lapped to the proper depth so as to attain the finalstripe and throat heights for the magnetic transducer and to attain thedesired contour 19 as shown in FIG. 2d. The resultant assembly isillustrated in FIG. 2e.

The conventional shape of FIG. 2 comprises a cylindrical or complexcontour which is critical in maintaining the moving tape in contact withthe transducer, as described above. The full width contour of FIGS. 1and 2 serves three purposes. 1) It prevents tape steering as therecording element is moved to access different data tracks. 2) Itprovides support for the tape as the head is positioned near the edge ofthe tape 13. and 3) It prevents the edges of the chip 14 from damagingthe tape. 13.

The contour of the head must also allow a low tension on the tape so asto not distort the tape. Typically, the contour is designed with a smallradius 19 in FIG. 2d so the pressure on the head, which is proportionalto the tape tension per unit width divided by the radius (T/wR), is highwith tensions low enough not to excessively distort the tape. However,the contour of the head must be such that the pressure of the tape onthe transducer is not so high that the surface of the transducer wearsexcessively.

Such full width heads are often provided with “outriggers” to maintain asmall wrap angle over the recording elements of the head even though thewrap angle over the outriggers can change with different cartridgesinserted into the tape drive. A change in wrap angle over the portion ofthe head containing the recording elements can lead to air entrainmentand excessive flying height of the tape.

Like the head assembly, the outriggers must also be the full width ofthe tape in order to prevent distortion of the tape. Often, theoutriggers must also be lapped to a contour which is coordinated withthe contour of the head assembly.

Individual lapping of the tape head assembly and of the correspondingoutriggers, especially to a contour, is very expensive and is a majorcontributor to the manufacturing cost of the tape head.

Partial span recording heads are used in helical scan tape recording andin floppy disks. They are individually assembled and then provided witha spherical or elliptical contour. Such heads have not been used inlinear tape recorders due to the need for tape edge support and arequirement for substantial tape tension or contact pressure to maintaincontact with the head. In addition, it is difficult to provide such acontour when a multiplicity of recording elements are required in thehead.

U.S. Pat. No. 4,123,791, Rotter et al., describes a single elementnarrow tape head positioned between outrigger bars of 0.25 inch radiuswith radial centers 0.4 inch apart. An additional pair of stuboutriggers aligned in the direction of tape travel, having the sameshape as the head and spaced 25 to 30 mils on either side of the head,were required to support the edge of the tape. The narrow tape head andstub outriggers were required to allow the splitting and passage of theboundary layer of air.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a tape head that doesnot require or complex assembly with stub outriggers.

Another object of the present invention is to provide a tape head whichattains optimum spacing with respect to the tape at all track positionsacross the width of tape.

Disclosed is a dimple magnetic recording head in a transducer assemblyfor linear tape drives. The dimple head has a flat transducing surfaceextending laterally a partial width of the magnetic recording tape. Twoparallel tape support surfaces extend laterally the full width of themagnetic recording tape, positioned on either side of and spaced fromthe dimple head in the longitudinal direction of the magnetic recordingtape. In addition, the anticlastic lift off of the tape near its edgesis minimized with present tape thickness (approx. 9 microns) and tensionfor a dimple head length of 0.6 to 1 mm in the tape moving direction.Further miminization can be achieved by providing a slight contour onthe edges of the dimple head. The tape support surfaces form a plane,and the dimple head flat transducing surface is parallel to the tapesupport surface plane and projects above the tape support surface planeto form tape wrap angles with respect to the tape support surfaces ofapproximately ½ degree to 2.5 degrees. The low wrap angle helps preventtape steering as the head is moved to access different data tracks. Thehigh end of the range (2.0 to 2.5 degrees) of wrap angle allows readingand writing nearer the edge of the tape at the expense of increased tapesteering.

A method for forming a dimple magnetic tape head is disclosed. Aplurality of transducers are formed on a common row of substrateelements, and the common row of substrate elements is lapped to achievethe proper throat height of the inductive write elements (approx ½ to 3microns), appropriate magnetoresistive stripe height of themagnetoresistive read elements (approx ½ to 3 microns), and a flattransducing surface. This is the most critical and expensive lappingstep in forming tape heads. With this disclosure a plurality ofrecording heads are lapped in a single rowbar in a single step thusreducing cost. The rowbar is subsequently diced into separate recordingheads, each of which may contain a multiplicity of recording elements.The two parallel, spaced apart tape support surfaces are provided, andone of the diced substrate elements is mounted intermediate the tapesupport surfaces with the flat transducing surface exposed for forming atape facing surface.

Other objects, features, and advantages of the present invention will beapparent from the accompanying drawings and from the detaileddescription below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures by the accompanying drawings in which likereferences indicate similar elements and in which:

FIG. 1 is a perspective illustration of a linear tape head assembly ofthe prior art;

FIGS. 2a through 2 e are illustrations of the method for producing theprior art linear tape head assembly of FIG. 1;

FIG. 3 is a perspective illustration of an embodiment of the linear tapehead of the present invention;

FIG. 4 is a perspective illustration of an embodiment of the linear tapehead assembly of the present invention;

FIG. 5 is an illustration of a cross section of the linear tape headassembly of FIG. 4;

FIG. 6 is a perspective illustration of a row of substrate elements withtransducers;

FIG. 7 is a diagrammatic illustration of a lapping system for lappingthe common row of substrate elements of FIG. 6;

FIG. 8 is a top view illustration of a substrate element diced from thecommon row of FIG. 6;

FIGS. 9a, 9 b and 9 c are top view illustrations of alternativeembodiments of substrate elements of the present invention;

FIG. 10 is a perspective illustration of an alternative embodiment of alinear tape head assembly of the present invention;

FIG. 11 is an illustration of a cross section of another alternativeembodiment of a linear tape head assembly of the present invention;

FIG. 12 is a perspective illustration of a movable head embodiment ofthe linear tape head assembly of the present invention;

FIG. 13 is an illustration of a cross section of the linear tape headassembly of FIG. 12;

FIG. 14 is an illustration of a cross section of an alternativeembodiment of the linear tape head assembly of FIG. 12; and

FIG. 15 is a diagrammatic illustration of a tape drive which mayincorporate the linear tape head assembly of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 illustrates an embodiment of the partial span tape head 20 of thepresent invention. Tape head 20 is a partial span flat head, called a“dimple” head, because the recording elements are located about centeredin a flat carrier. The head can be batch fabricated by stripe and throatheight lapping then diced and assembled into carriers to providecompleted heads. A row of heads is lapped to achieve the proper throatheight of the inductive write elements (approx ½ to 3 microns),appropriate magnetoresistive stripe height of the magnetoresistive readelements (approx ½ to 3 microns), and a flat transducing surface. Thisis the most critical and expensive lapping step in forming tape heads.With this disclosure a plurality of recording heads are lapped in asingle rowbar in a single step thus reducing cost. The rowbar issubsequently diced into separate recording heads, each of which maycontain a multiplicity of recording elements.

The head 20 slightly penetrates the plane of the tape 21 to provide asmall wrap angle for scraping the air off as it goes by the sharp edge.Cable 22 connects the dimple tape head 20 to the read/write channel ofan associated tape drive.

Dimple tape head 20 works properly over only a small range of wrapangles. For one embodiment, the range of wrap angle is from about ½degree to 2.5 degrees.

Because of the very small wrap angle, the head does very little tapesteering as it moves from one side of the tape 21 to the other to accessthe recording tracks. In addition, the anticlastic liftoff of the tapenear its edges is minimized with present tape thickness (approx. 9microns) and tension for a dimple head length of 0.6 to 1 mm in the tapemoving direction. Further minimization can be acheived by providing aslight contour on the edges of the dimple head.

FIG. 4 illustrates one embodiment of the tape head assembly whichincludes linear dimple tape head 20 with outriggers 24 and 25.Outriggers 24 and 25 maintain the proper wrap angle and prevent tapesteering by extending the full width of the tape 21.

For one embodiment, a wrap angle between about ½ degree and 2.5 degreesis adequate to scrape the air off the tape and to provide the desiredspacing between the tape and the transducer elements in the dimple head.Surfaces 26 of the outriggers 24 and 25 provide a convenient means ofcontrolling the wrap angle.

FIG. 5 is a cross sectional view of the linear dimple tape head assemblyof FIG. 4. For one embodiment, the size of the wrap angle may beprecisely controlled by lapping flat surfaces 26 of the outriggers 24and 25 to a precise dimension in a common plane, and then mounting thedimple head 20 in a plane parallel to the plane formed by the surfaces26 at a precise height with respect to the plane formed by the flatsurfaces 26. In a preferred embodiment, a penetration of the flatsurface 27 of dimple head 20 above the plane of the flat outriggersurfaces 26 of the order of 0.001 inch (1 mil) is adequate to obtain thedesired wrap angle and transducer to tape spacing.

FIG. 6 illustrates a row 30, or rowbar, cut from a substrate or waferalong with a closure 31. The transducers are mass produced usingconventional etching and deposition techniques. The row 30 is typicallyformed on a ceramic substrate which is either magnetic, such as ferrite,or non-magnetic such as Alumina-Titanium-Carbide depending on thedesign. The write and read heads are formed on the substrate usingconvention thin film deposition, etching, and lithographic techniques.Both the inductive write elements and magnetoresistive read elements areprovided with connection terminal 32. Closure 31 is provided to protectthe thin film read and write elements from being damaged by the tape andto form part of the flat transducing surface. As illustrated in FIG. 6,underside surface 33 of the row 30 and closure 31 is the transducingsurface and is lapped to achieve the final throat and stripe heights ofthe transducers.

A typical lapping system for lapping flat transducing surface 33 ofcommon row 30 is illustrated in FIG. 7. A lapping fixture 40 holds thecommon row 30 of substrate elements in position over a lapping plate 41.Lapping plate 41 is a flat abrasive surface for accurately lappingsurface 33 to a final dimension.

The force applied to lapping fixture 40 is derived from first and secondpressure actuators 43 and 44. Varying the force applied by the actuators43 and 44 against substrate row 30 controls leveling of the lappedsurface 33.

The lapping device insures thereby insuring that the throat heights andstripe heights for all of the transducers are at the same length.

After completion of lapping of row transducer surface 33, row 30 isdiced or partitioned into separate dimple heads. The mass production ofthe dimple heads as described above substantially reduces the cost ofproviding lapped heads, as compared to the individual lapping requiredby the prior art.

A single dimple head is illustrated in FIG. 8. Substrate 50, closure 51and gap 52 form flat transducing surface 27 of the dimple head. In apreferred embodiment, a plurality of read and write elements arecontained in gap 52.

FIGS. 9a-c illustrate alternative embodiments of the dimple head. FIG.9a shows a square head embodiment with sharp corners 55. Although thesharp corners 55 may be effective in scraping the boundary layer of airfrom the tape, the tape exerts its greatest pressure on the corners.FIG. 9b shows a dimple head with rounded corners, called “edge blend”,to minimize edge pressure when used with a carrier like that of FIG. 4.The corners are rounded after the head has been diced from the commonrow.

FIG. 9c shows a round configuration which reduces the edge pressure whenused with the carrier of FIG. 10. Other shapes, such as those of FIGS.9a and 9 b may also be used. The dimple head 60 is still flat, but iscircular in the other dimension. The dimple head is rounded after thehead has been diced from the row. Outriggers 61 and 62 are joined byflat surfaces 63, and the head is placed in a circular cutout so as toprotrude slightly so that tape 65 forms a wrap angle of betweenapproximately ½ degree and 2.5 degrees with respect to the edges formedby outriggers 61 and 62 with flat surface 63. Outrigger flat surface 63may be lapped or ground to a common plane.

FIG. 11 illustrates an alternative embodiment of the present inventionhaving a dimple head 66 and outrigger dowels 67 mounted in a carrier 68.The dimple head 66 is mounted so as to protrude slightly above theoutrigger dowels 67 and 68 and penetrate into tape 69 sufficiently toform a wrap angle of between approximately ½ degree and 2.5 degrees.

FIG. 12 illustrates an alternative embodiment of a linear tape headassembly of the present invention having a fixed set of outriggers 70and a moveable head 71. The outriggers 70 extend the full width of tape72, while head 71 moves in the lateral direction between tracks.

FIG. 13 is a cross section view of the linear tape head assembly of FIG.12, illustrating the slight penetration of the head 71 into the tape 72above outriggers 70. The slight penetration by head 71 provides a wrapangle of tape 72 of between about ½ degree and 2.5 degrees. Theoutriggers 70 maintain the proper wrap angle and prevent tape steeringby the movement of the head 71. Single recording gap 73 is provided inhead 71, which may include a multiplicity of transducers.

FIG. 14 illustrates a moveable read after write head 76 having dualrecording gaps. Head 76 comprises two heads 71 whose flat transducingsurfaces 77 slope down from the center ½ to 1 degree each. The wrapangle of tape 72 is provided by outriggers 70 in the range between about½ degree and 2.5 degrees with respect to each side of the head 76. Readafter write head 76 may also be employed in any of the embodiments ofthe invention.

FIG. 15 illustrates an embodiment of a tape drive 80 incorporatingdimple head assembly 81. A tape drive control unit 82 provides a motorcontrol signal to rotate tape reels 83 and move tape 84 across thedimple head assembly 81. Read/write channel 86 amplifies, decodes orencodes, and transmits read signals from the dimple head and/or writesignals to the dimple head with respect to control unit 82. The data iscommunicated through I/O channel 87 with host 88. Lateral repositioningof the dimple head assembly 81 with respect to the tape 84 isaccomplished by positioning actuator 90. The lateral repositioning isrequired to access the various tracks of the tape 84 with the dimplehead 81. A servo system may be employed for accurate lateralrepositioning of the head assembly 81. An exemplary servo systemincludes a servo detector 91 to detect both the track that the head iscurrently on and whether the head is off center. Control unit 82indicates the track address of a desired new track to position errordetection controller 93 for repositioning the head. Servo detector 91indicates the current track to position error detection controller 93,and the controller provides a servo position error signal to positioningactuator 90 which repositions the dimple head assembly 81 to the newtrack. The servo system also provides track following signals topositioning actuator 90 so that the tracks on tape 84 may be closelyspaced.

Alternatively, positioning actuator 90 may comprise a stepping motorwhich repositions the dimple head assembly 81 between fixed positions.These and other repositioning means are within the skill of thoseskilled in the art.

Outriggers of the dimple head assembly 81 support the tape 84 in alllateral positions of the dimple head transducer across the tape andmaintain the wrap angle of the tape with respect to the dimple head.

While the preferred embodiments of the present invention have beenillustrated in detail, it should be apparent that modifications andadaptations to those embodiments may occur to one skilled in the artwithout departing from the scope of the present invention as set forthin the following claims.

We claim:
 1. A method for forming a linear magnetic tape head from oneof a row of transducers formed on a substrate, said tape head for usewith a magnetic recording tape, comprising the steps of: lapping saidsubstrate to form an entirely substantially flat transducing surface foreach of said transducers of said row, said entirely substantially flattransducing surface extending to laterally extending edges thereof, andforming substantially a right angle therewith; dicing said row from saidsubstrate into separate substrate elements, each diced substrate elementhaving at least one of said transducers, said diced substrate elemententirely substantially flat transducing surface extending laterally apartial width of said magnetic recording tape; providing two parallel,spaced apart outrigger tape elements having parallel outrigger tapesupport surfaces in a common plane, said outrigger tape support surfaceseach extending laterally a distance greater than said flat transducingsurface partial width and the full width of said magnetic recordingtape; and mounting one of said diced substrate elements intermediate andspaced from said outrigger tape support surfaces, and within boundsformed by said outrigger tape support surfaces, with said entirelysubstantially flat transducing surface exposed for forming a tape facingsurface.
 2. The method for forming a linear magnetic tape head of claim1, wherein said step of providing outrigger tape elements with outriggertape support surfaces additionally comprises the step of lapping orgrinding said tape support surfaces to said common plane, said commonplane tape support surfaces each extending laterally said full width ofsaid magnetic recording tape.